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Howard Lam says he was warned against trying to engage with Liu Xia

A veteran democracy activist in Hong Kong says he was kidnapped, beaten and tortured by agents of mainland China after trying to get in touch with Liu Xia, the widow of Nobel Peace Prize winner Liu Xiaobo.

The activist, Howard Lam, said on his Facebook page in late July that he had obtained a signed photo of the Barcelona football player Lionel Messi, and that he intended to send it to Ms Liu as a condolence gift.

Liu Xiaobo, who died from liver cancer in July, was a big fan of the football star.

Earlier this week, Mr Lam said he had received a phone call from an old acquaintance working for the Chinese security services who warned him to stay away from Ms Liu, who is believed to be under continued house arrest.

The activist said he was abducted on Thursday afternoon in the bustling neighbourhood of Mongkok by unknown men speaking Mandarin Chinese - spoken in the mainland but far less common in Cantonese-speaking Hong Kong.

WARNING: This article contains a close up image of the injury.

"They gave me a warning," said Mr Lam. "They wanted to alert so many people that if you don't love China, your government, you may have the chance of something like this happening."

He said he had been rendered unconscious by a chemical applied to his nose and mouth. After he regained consciousness, he was being beaten around the torso and tortured with a stapler.

He said the men taunted him, saying they were making crosses with the metal staples because the activist was a Christian. Eventually, he fainted again.

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Mr Lam says the men used a stapler to make crosses in his legs

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Mr Lam says he wanted to send a signed photo to Liu Xiaobo's widow

When he came to shortly after midnight, he found himself on a beach in eastern Hong Kong and made his way to a taxi.

The first thing Mr Lam did on Friday morning was to give a news conference, before heading to hospital for treatment, where he was questioned by police officers.

When asked about the case, police commissioner Stephen Lo said the allegations were serious and that the investigation had begun.